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Since the 1st of July 1995, a European regulation came into effect across the European territory.
According to the chart below, the standard has defined different protection categories. These are classified in terms of the lens ability to absorb the light. For each of them a minimum UV filtration is required. Although most lenses ensure 100% protection from UVA-B to 380 nm (hence the common name UV400), the filter choice must above all be selected according to the environment and sunlight.
|21% - 57%||Poor sunlight|
|58% - 82%||Average solar luminosity|
|83% - 92%||Strong sunlight|
|93% - 97%||Very strong sunlight|
In the mountains the atmosphere filters decreases with altitude; the sun attacks those who are not sufficiently equipped to face it. For each 1000 meters level gained in altitude, the ambient UV proportion increases by 10%. Solar radiation is extremely important in winter because the snow reflects 80% of UV, while the sea will proportionately reflect 20%. Therefore, it is advisable to wear sunglasses to filter UV (category 4) in high mountain (category 3) in outdoor activities, with enveloping lenses to avoid reflected radiation.
The protection category of sunglasses lenses is an essential feature of an optimal vision during sun exposure.
The category number will determine the percentage of visible light and filtered light as shown here after.
These are lightly tinted sunglasses that filter between 21 and 57% of the solar luminosity. This type of index is recommended for reduced sunlight situations, when the weather is overcast. This type of index is not recommended for massive exposure to strong sunlight.
Your sunglasses will filter 58% to 82% of solar ambient luminosity. This protection will be effective in average sunshine situations.
This filter is perfect for most sunshine situations. Your sunglasses will filter 83-92% of the solar luminosity. These will give you, in the majority of your activities, an excellent optical sun protection against solar radiation and glare. This protection is particularly effective in strong sunlight situations.
This filter is the most powerful of all. It can filter up to 97% brightness. It is generally used for extreme solar luminosity, for example: mountaineering on glaciers, in high mountain mainly because of the brightness intensified by the reflection on the ice and snow. This solar filter index is forbidden for driving because it distorts optical colour vision and perception.